1. Field of the Invention
This invention relates to a method of applying a decorative coating onto a glass pane by the screen printing process, wherein the decorative coating, at least in a selected region, is applied right up to the peripheral edge of the glass pane. The invention relates also to devices for carrying out the method.
2. Description of the Related Art
Automobile glazing panes are frequently provided along one edge or along the entire periphery thereof with a decorative coating, usually of a baking finish. This decorative coating has, amongst other things, the function of protecting the adhesive film by which the glass panes are fixed in the frame from UV radiation. For applying the decorative coating onto the glass surface, the silk screen printing process has proved especially suitable. The printing ink is usually baked in at temperatures of 550 to 600 degrees Celsius or higher in the course of the heat treatment required for the curving and/or toughening of the glass panes.
The glass panes in the installed condition are now frequently no longer covered by a profiled frame encompassing the pane at the edge or fitting over the edge, but instead the glass panes are visible from the outside right up to their edges. This means that the decorative print at the edge is also visible right up to the periphery of the glass pane. Irregularities in the outer boundary of the decorative coating, especially slightly differing distances between the outer boundary of the decorative coating and the edge of the glass pane, can have a very adverse appearance. Furthermore, in the regions that are free of the decorative coating, the protection of the adhesive film from ultraviolet radiation is no longer provided. A considerable interest therefore exists in being able to print the colored coating forming the decorative coating in selected regions or along the entire periphery of the glass pane, right up as far as the peripheral edge.
In the usual printing processes, especially in screen printing, it is difficult for various reasons to carry out an exact color application accurately right up to the edge of the glass pane. The glass panes as a rule have certain admissible dimensional tolerances, whereas they are all printed using the same printing screen. The positioning operations of the glass panes to be printed and of the printing tools are also accompanied by tolerances, which may be additive to the dimensional tolerances of the glass panes. If the part of the printing screen permeable to the printing ink projects beyond the edge of the glass pane, the printing ink adheres in the meshes of the printing screen and on the underside of the printing screen at these locations, which leads to unclear printed images in the succeeding printing operations. To overcome this difficulty, therefore, the application of the color in the screen printing process is usually performed only up to a distance from the edge of the pane which allows for the most unfavorable case.
It is known to obtain, by the screen printing process, a decorative coating extending up to the edge of the pane by laying templates complementary to the shape of the glass pane against the pane and carrying out the color application beyond the edge of the pane and onto the surfaces of these templates, which are then removed from the glass pane (U.S. Pat. No. 4,268,545). When the templates are removed from the glass pane edge, however, the printed ink has not yet dried and can foul the peripheral face of the glass pane. Furthermore, the printing ink on the templates has not yet dried at the next succeeding printing operation and transfers onto the lower face of the printing screen.